Fair question. Obviously, you need a preamp if your amp has no volume control and you want to use more than one source and want to conveniently select between them with a switch. With some sources, you might need amplification to get to line level. Phono, for vinyl and MC or MM cartridges and no phono preamp, some digital sources (I remember an Apple Airport I used as a streamer some years ago needing quite a bit of volume addition from my Rotel Receiver.) If you want to use headphones but don't want to have a dedicated headphone amp, a preamp can provide. These days, other devices have assumed some of the preamp functions, so you could make do without a separate preamp. Many streamers have DACs and preamp volume, bass, treble and balance functions of classic preamps in their phone apps, some even have phono preamps and headphone amps with headphone jacks, functions which duplicate or replace those typically on a preamp. Depending on your use case, the need for a preamp could range from not at all to essential.
Preamp - what's the purpose?
Intentionally dumb question...
I've heard various 5-15W tube amps in my room. EL84, 300B, etc. They all have input stages and the output stage. I send them a line-level signal from a DAC.
Sitting a few meters away from my loudspeakers, the first watt alone gives me roughly 80db of volume. I think these amps are biased to expect the line level signal directly. Why wouldn't the designer do that?
So what's the point of adding a pre-amp? Why do people do it?
thanks in advance